1. Field of the Invention
The present invention relates to a corrosion detection circuit for a circuit board and a motor drive having the corrosion detection circuit, and more specifically relates to a corrosion detection circuit that includes a test chip having a corrodible metal, resistors having high resistance values, and a voltage detection circuit to enable the detection of the risk of corrosion by a corrosive liquid or gas in advance without applying a specific coating material or forming a specific resist, and a motor drive having the corrosion detection circuit.
2. Description of Related Art
Motor drives have the problem that cutting fluids, cleaning fluids, and other liquids and gases used in factories cause corrosion of electronic components and circuit boards, thus impairing necessary functions. As a measure against the problem, there is a method in which a test chip having a corrodible metal is arranged on the circuit boards and the resistance value thereof is monitored to issue an alarm before impairing the functions of the circuits. However, this method may detect a variation in the resistance value due to environmental factors such as a finger contacting the test chip or the adhesion of dust to the test chip. It is not necessary to detect such a variation in the resistance value for the motor drives.
As a diagnosis device for a circuit board having an electronic component thereon to solve the above problem, there is known an environment diagnosis device for electrical equipment in which a detection conductive material of a test chip is covered with a silicone coating material having water absorbability and gas permeability to prevent the adhesion of dust to the detection conductive material and a finger contact therewith (for example, Japanese Unexamined Patent Publication (Kokai) No. 10-300699, hereinafter referred to as “patent literature 1”).
A malfunction detection circuit in which a sub pattern, which is wired in a part of a circuit board as a circuit for detecting a break in a wiring pattern formed on the circuit board due to corrosion and a short in the wiring pattern due to migration to detect a malfunction in the circuit board, is covered with a sub resist that is thinner than the thickness of a solder resist for covering the other portions is known. The sub pattern has traces arranged in parallel at predetermined intervals (for example, Japanese Unexamined Patent Publication (Kokai) No. 2009-216391, hereinafter referred to as “patent literature 2”).